Electric heat treat furnaces employing molten salt baths within which workpieces may be suspended for heat treatment are known and wherein, the pairs of electrodes employed are normally emersed within the bath adjacent the bottom of the chamber. These are ineffective in maintaining a uniform temperature throughout the depth of the bath. This is particularly true as heat treat baths increase in depth. There is a limit to which heat convection from electrodes spaced near the bottom of such bath will be effective for providing uniform heat treat temperatures throughout the height of the bath.
Heretofore, variations in temperature have exceeded 75 degrees F. between top and bottom in typical 80-inch deep baths. There has, therefore, existed the problem of maintaining a substantially uniform temperature throughout the depth of the bath to provide for uniform heat treatment of workpieces suspended therein.
Heretofore, in old salt bath designs, the entrant opening has been maintained as small as possible in order to minimize radiation losses. Hence the bath has been made deeper normally so that the work is arranged above the current electrode paths. In cases where too deep a bath is required, the bath has been made wider so that the full bath depth can be utilized at the expense of increased radiation losses.
Heretofore, there has been another problem in the placement of electrodes such that, it has not been possible for workpieces to occupy the full dimensions of the bath laterally and longitudinally without obstructing a portion of the electron bath between electrodes.
Examples of prior art patents related to the present heat treat furnace may be found in the following U.S. Pat. Nos. 2,355,761, 3,049,576, 3,128,327, 3,420,937, 3,085,124, 2,464,008, 2,213,138, 2,820,075, 3,770,501, and 2,249,993.